Attempts are being made to increase the capacity of optical data transmission systems, which usually employ amplitude modulation of an optical carrier wave. There are many research projects at the present time seeking to develop simultaneous transmission of data addressed to the largest possible number of users.
Routing data by means of wavelength division multiplexers has the advantage of being passive. However, to obtain the full benefit of this advantage, it is advisable to modify the carrier wavelengths assigned to each addressee as soon as needed. The time to switch from one wavelength to another is referred to as the tuning time and must be as short as possible.
A solution providing a generator of optical data carrier signals with selectable carrier wavelengths described in the paper “RINGO: a WDM ring optical packet network demonstrator”, R. Gaudino et al., Th.L.2.6, ECOC′2001, September 2001, uses as many constant wavelength laser sources as there are wavelengths that can be used, the sources feeding an optical multiplexer. Thus a signal at a chosen wavelength is injected into an optoelectronic modulator which forms a data carrier signal to be sent to an associated addressee.
Because the number of laser sources is proportional to the number of addressees, a device of the above kind is costly, consumes too much power, and is difficult to integrate into existing optical transmission systems such as optical routing systems and communication nodes of metropolitan area networks, which nodes are getting progressively smaller.